Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull RCU changes from Ingo Molnar:
 "The main changes in this cycle were:

   - Improvements to expedited grace periods (Paul E McKenney)

   - Performance improvements to and locktorture tests for percpu-rwsem
     (Oleg Nesterov, Paul E McKenney)

   - Torture-test changes (Paul E McKenney, Davidlohr Bueso)

   - Documentation updates (Paul E McKenney)

   - Miscellaneous fixes (Paul E McKenney, Boqun Feng, Oleg Nesterov,
     Patrick Marlier)"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (54 commits)
  fs/writeback, rcu: Don't use list_entry_rcu() for pointer offsetting in bdi_split_work_to_wbs()
  rcu: Better hotplug handling for synchronize_sched_expedited()
  rcu: Enable stall warnings for synchronize_rcu_expedited()
  rcu: Add tasks to expedited stall-warning messages
  rcu: Add online/offline info to expedited stall warning message
  rcu: Consolidate expedited CPU selection
  rcu: Prepare for consolidating expedited CPU selection
  cpu: Remove try_get_online_cpus()
  rcu: Stop excluding CPU hotplug in synchronize_sched_expedited()
  rcu: Stop silencing lockdep false positive for expedited grace periods
  rcu: Switch synchronize_sched_expedited() to IPI
  locktorture: Fix module unwind when bad torture_type specified
  torture: Forgive non-plural arguments
  rcutorture: Fix unused-function warning for torturing_tasks()
  rcutorture: Fix module unwind when bad torture_type specified
  rcu_sync: Cleanup the CONFIG_PROVE_RCU checks
  locking/percpu-rwsem: Clean up the lockdep annotations in percpu_down_read()
  locking/percpu-rwsem: Fix the comments outdated by rcu_sync
  locking/percpu-rwsem: Make use of the rcu_sync infrastructure
  locking/percpu-rwsem: Make percpu_free_rwsem() after kzalloc() safe
  ...

include/linux/cpu.h

@@ -228,7 +228,6 @@ extern struct bus_type cpu_subsys;
 extern void cpu_hotplug_begin(void);
 extern void cpu_hotplug_done(void);
 extern void get_online_cpus(void);
-extern bool try_get_online_cpus(void);
 extern void put_online_cpus(void);
 extern void cpu_hotplug_disable(void);
 extern void cpu_hotplug_enable(void);
@@ -246,7 +245,6 @@ int cpu_down(unsigned int cpu);
 static inline void cpu_hotplug_begin(void) {}
 static inline void cpu_hotplug_done(void) {}
 #define get_online_cpus()	do { } while (0)
-#define try_get_online_cpus()	true
 #define put_online_cpus()	do { } while (0)
 #define cpu_hotplug_disable()	do { } while (0)
 #define cpu_hotplug_enable()	do { } while (0)

include/linux/list.h

@@ -87,7 +87,7 @@ static inline void list_add_tail(struct list_head *new, struct list_head *head)
 static inline void __list_del(struct list_head * prev, struct list_head * next)
 {
 	next->prev = prev;
-	prev->next = next;
+	WRITE_ONCE(prev->next, next);
 }
 
 /**
@@ -615,7 +615,8 @@ static inline void __hlist_del(struct hlist_node *n)
 {
 	struct hlist_node *next = n->next;
 	struct hlist_node **pprev = n->pprev;
-	*pprev = next;
+
+	WRITE_ONCE(*pprev, next);
 	if (next)
 		next->pprev = pprev;
 }

include/linux/list_bl.h

@@ -93,9 +93,10 @@ static inline void __hlist_bl_del(struct hlist_bl_node *n)
 	LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
 
 	/* pprev may be `first`, so be careful not to lose the lock bit */
-	*pprev = (struct hlist_bl_node *)
+	WRITE_ONCE(*pprev,
+		   (struct hlist_bl_node *)
 			((unsigned long)next |
-			 ((unsigned long)*pprev & LIST_BL_LOCKMASK));
+			 ((unsigned long)*pprev & LIST_BL_LOCKMASK)));
 	if (next)
 		next->pprev = pprev;
 }

include/linux/list_nulls.h

@@ -76,7 +76,8 @@ static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
 {
 	struct hlist_nulls_node *next = n->next;
 	struct hlist_nulls_node **pprev = n->pprev;
-	*pprev = next;
+
+	WRITE_ONCE(*pprev, next);
 	if (!is_a_nulls(next))
 		next->pprev = pprev;
 }

include/linux/percpu-rwsem.h

@@ -5,11 +5,12 @@
 #include <linux/rwsem.h>
 #include <linux/percpu.h>
 #include <linux/wait.h>
+#include <linux/rcu_sync.h>
 #include <linux/lockdep.h>
 
 struct percpu_rw_semaphore {
+	struct rcu_sync		rss;
 	unsigned int __percpu	*fast_read_ctr;
-	atomic_t		write_ctr;
 	struct rw_semaphore	rw_sem;
 	atomic_t		slow_read_ctr;
 	wait_queue_head_t	write_waitq;

include/linux/rcu_sync.h

@@ -0,0 +1,86 @@
+/*
+ * RCU-based infrastructure for lightweight reader-writer locking
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, you can access it online at
+ * http://www.gnu.org/licenses/gpl-2.0.html.
+ *
+ * Copyright (c) 2015, Red Hat, Inc.
+ *
+ * Author: Oleg Nesterov <oleg@redhat.com>
+ */
+
+#ifndef _LINUX_RCU_SYNC_H_
+#define _LINUX_RCU_SYNC_H_
+
+#include <linux/wait.h>
+#include <linux/rcupdate.h>
+
+enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
+
+/* Structure to mediate between updaters and fastpath-using readers.  */
+struct rcu_sync {
+	int			gp_state;
+	int			gp_count;
+	wait_queue_head_t	gp_wait;
+
+	int			cb_state;
+	struct rcu_head		cb_head;
+
+	enum rcu_sync_type	gp_type;
+};
+
+extern void rcu_sync_lockdep_assert(struct rcu_sync *);
+
+/**
+ * rcu_sync_is_idle() - Are readers permitted to use their fastpaths?
+ * @rsp: Pointer to rcu_sync structure to use for synchronization
+ *
+ * Returns true if readers are permitted to use their fastpaths.
+ * Must be invoked within an RCU read-side critical section whose
+ * flavor matches that of the rcu_sync struture.
+ */
+static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
+{
+#ifdef CONFIG_PROVE_RCU
+	rcu_sync_lockdep_assert(rsp);
+#endif
+	return !rsp->gp_state; /* GP_IDLE */
+}
+
+extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type);
+extern void rcu_sync_enter(struct rcu_sync *);
+extern void rcu_sync_exit(struct rcu_sync *);
+extern void rcu_sync_dtor(struct rcu_sync *);
+
+#define __RCU_SYNC_INITIALIZER(name, type) {				\
+		.gp_state = 0,						\
+		.gp_count = 0,						\
+		.gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait),	\
+		.cb_state = 0,						\
+		.gp_type = type,					\
+	}
+
+#define	__DEFINE_RCU_SYNC(name, type)	\
+	struct rcu_sync_struct name = __RCU_SYNC_INITIALIZER(name, type)
+
+#define DEFINE_RCU_SYNC(name)		\
+	__DEFINE_RCU_SYNC(name, RCU_SYNC)
+
+#define DEFINE_RCU_SCHED_SYNC(name)	\
+	__DEFINE_RCU_SYNC(name, RCU_SCHED_SYNC)
+
+#define DEFINE_RCU_BH_SYNC(name)	\
+	__DEFINE_RCU_SYNC(name, RCU_BH_SYNC)
+
+#endif /* _LINUX_RCU_SYNC_H_ */

include/linux/rculist.h

@@ -247,10 +247,7 @@ static inline void list_splice_init_rcu(struct list_head *list,
  * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
  */
 #define list_entry_rcu(ptr, type, member) \
-({ \
-	typeof(*ptr) __rcu *__ptr = (typeof(*ptr) __rcu __force *)ptr; \
-	container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member); \
-})
+	container_of(lockless_dereference(ptr), type, member)
 
 /**
  * Where are list_empty_rcu() and list_first_entry_rcu()?

include/linux/rcupdate.h

@@ -160,7 +160,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
  * more than one CPU).
  */
 void call_rcu(struct rcu_head *head,
-	      void (*func)(struct rcu_head *head));
+	      rcu_callback_t func);
 
 #else /* #ifdef CONFIG_PREEMPT_RCU */
 
@@ -191,7 +191,7 @@ void call_rcu(struct rcu_head *head,
  * memory ordering guarantees.
  */
 void call_rcu_bh(struct rcu_head *head,
-		 void (*func)(struct rcu_head *head));
+		 rcu_callback_t func);
 
 /**
  * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
@@ -213,7 +213,7 @@ void call_rcu_bh(struct rcu_head *head,
  * memory ordering guarantees.
  */
 void call_rcu_sched(struct rcu_head *head,
-		    void (*func)(struct rcu_head *rcu));
+		    rcu_callback_t func);
 
 void synchronize_sched(void);
 
@@ -274,7 +274,7 @@ do {									\
  * See the description of call_rcu() for more detailed information on
  * memory ordering guarantees.
  */
-void call_rcu_tasks(struct rcu_head *head, void (*func)(struct rcu_head *head));
+void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
 void synchronize_rcu_tasks(void);
 void rcu_barrier_tasks(void);
 
@@ -297,12 +297,14 @@ void synchronize_rcu(void);
 
 static inline void __rcu_read_lock(void)
 {
-	preempt_disable();
+	if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
+		preempt_disable();
 }
 
 static inline void __rcu_read_unlock(void)
 {
-	preempt_enable();
+	if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
+		preempt_enable();
 }
 
 static inline void synchronize_rcu(void)
@@ -535,28 +537,8 @@ static inline int rcu_read_lock_sched_held(void)
 
 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 
-/* Deprecate rcu_lockdep_assert():  Use RCU_LOCKDEP_WARN() instead. */
-static inline void __attribute((deprecated)) deprecate_rcu_lockdep_assert(void)
-{
-}
-
 #ifdef CONFIG_PROVE_RCU
 
-/**
- * rcu_lockdep_assert - emit lockdep splat if specified condition not met
- * @c: condition to check
- * @s: informative message
- */
-#define rcu_lockdep_assert(c, s)					\
-	do {								\
-		static bool __section(.data.unlikely) __warned;		\
-		deprecate_rcu_lockdep_assert();				\
-		if (debug_lockdep_rcu_enabled() && !__warned && !(c)) {	\
-			__warned = true;				\
-			lockdep_rcu_suspicious(__FILE__, __LINE__, s);	\
-		}							\
-	} while (0)
-
 /**
  * RCU_LOCKDEP_WARN - emit lockdep splat if specified condition is met
  * @c: condition to check
@@ -594,7 +576,6 @@ static inline void rcu_preempt_sleep_check(void)
 
 #else /* #ifdef CONFIG_PROVE_RCU */
 
-#define rcu_lockdep_assert(c, s) deprecate_rcu_lockdep_assert()
 #define RCU_LOCKDEP_WARN(c, s) do { } while (0)
 #define rcu_sleep_check() do { } while (0)
 
@@ -810,6 +791,28 @@ static inline void rcu_preempt_sleep_check(void)
  */
 #define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
 
+/**
+ * rcu_pointer_handoff() - Hand off a pointer from RCU to other mechanism
+ * @p: The pointer to hand off
+ *
+ * This is simply an identity function, but it documents where a pointer
+ * is handed off from RCU to some other synchronization mechanism, for
+ * example, reference counting or locking.  In C11, it would map to
+ * kill_dependency().  It could be used as follows:
+ *
+ *	rcu_read_lock();
+ *	p = rcu_dereference(gp);
+ *	long_lived = is_long_lived(p);
+ *	if (long_lived) {
+ *		if (!atomic_inc_not_zero(p->refcnt))
+ *			long_lived = false;
+ *		else
+ *			p = rcu_pointer_handoff(p);
+ *	}
+ *	rcu_read_unlock();
+ */
+#define rcu_pointer_handoff(p) (p)
+
 /**
  * rcu_read_lock() - mark the beginning of an RCU read-side critical section
  *
@@ -1065,7 +1068,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
 #define __kfree_rcu(head, offset) \
 	do { \
 		BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
-		kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
+		kfree_call_rcu(head, (rcu_callback_t)(unsigned long)(offset)); \
 	} while (0)
 
 /**

include/linux/rcutiny.h

@@ -83,7 +83,7 @@ static inline void synchronize_sched_expedited(void)
 }
 
 static inline void kfree_call_rcu(struct rcu_head *head,
-				  void (*func)(struct rcu_head *rcu))
+				  rcu_callback_t func)
 {
 	call_rcu(head, func);
 }
@@ -216,6 +216,7 @@ static inline bool rcu_is_watching(void)
 
 static inline void rcu_all_qs(void)
 {
+	barrier(); /* Avoid RCU read-side critical sections leaking across. */
 }
 
 #endif /* __LINUX_RCUTINY_H */

include/linux/rcutree.h

@@ -48,7 +48,7 @@ void synchronize_rcu_bh(void);
 void synchronize_sched_expedited(void);
 void synchronize_rcu_expedited(void);
 
-void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
+void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func);
 
 /**
  * synchronize_rcu_bh_expedited - Brute-force RCU-bh grace period

include/linux/sched.h

@@ -1345,10 +1345,12 @@ struct sched_dl_entity {
 
 union rcu_special {
 	struct {
-		bool blocked;
-		bool need_qs;
-	} b;
-	short s;
+		u8 blocked;
+		u8 need_qs;
+		u8 exp_need_qs;
+		u8 pad;	/* Otherwise the compiler can store garbage here. */
+	} b; /* Bits. */
+	u32 s; /* Set of bits. */
 };
 struct rcu_node;
 

include/linux/srcu.h

@@ -215,8 +215,11 @@ static inline int srcu_read_lock_held(struct srcu_struct *sp)
  */
 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
 {
-	int retval = __srcu_read_lock(sp);
+	int retval;
 
+	preempt_disable();
+	retval = __srcu_read_lock(sp);
+	preempt_enable();
 	rcu_lock_acquire(&(sp)->dep_map);
 	return retval;
 }